1. Field of the Invention
The present invention relates to a wafer holding device which is used in the filmmaking, etching and exposure apparatuses in semiconductor manufacturing processes.
2. Prior Art
In the process of fabricating the semiconductor devices, various kind of wafer holding devices have been used for holding wafers, especially, semiconductor wafers, in the semiconductor treating apparatuses. such apparatuses include a filmmaking apparatus for forming thin films onto the wafers, a etching apparatus for micro-etching or cutting the surface of the wafers and an exposure apparatus for emitting light to the photo-resist resin attached on the wafer prior to etching.
For example, the wafer holding device having a stage made of ceramics are known, which has a top surface as a holding surface for mounting the wafer to be treated. A parallel electrode to the surface is buried in the ceramic body to attract the wafer to the wafer holding device due to attracting force such as Coulomb force by dielectric polarization and Johnson-Rahbeck force by the leakage current, by applying the direct current to the electrode. As another example, the device having an heating function of the buried electrode is also known, in which alternative current are supplied between the electrode and the wafer set on the surface to heat said wafer. Further, it is known that another device with plasma generating mechanism has another electrode together with the buried electrode and high frequency current is supplied therebetween to generate plasma. The wafer holding devices provided with all these functions and mechanisms also are known.
For these devices, non-uniform distribution of the temperature on the holding surface of the device greatly affects the precision of forming and treating of the wafers in each of filmmaking, etching and exposure steps during semiconductor manufacturing processes. Then, in order to control the temperature of the holding surface of the device, for some wafer holding devise, a metal base has been attached under the stage of a ceramics body, which has heating or cooling function.
As method of joining the metal stage and the ceramic base of the device, fastening them with bolts embedded in the ceramics and nuts screwed to the bolts passing through the plate has been adopted.
The Japanese Patent Publication No.JP-A 2-27748 discloses another method which adhere a stage and a metal base with an adhesive resin material.
However, in the method of fastening with bolts, it is easy to work for fastening but a clearance is apt to occur between the metal base and the ceramic stage, which reduce the heat transfer coefficient between the metal base and the ceramic stage in heating or cooling the stage.
In the method of adhering, since the heat conductivity of the adhesive, in general, is low, the device can not enhance enough in heat transfer characteristics in heating or cooling the stage, and can not be used above 150.degree. C., this temperature being almost near softening temperatures of the resin adhesives.
It may be considerable that another method of adhering the stage and base with the metal layer formed of metals such as molybdenum, tungsten, tantalum, nickel, etc., which can temper thermal expansion difference between the ceramic stage and metal base. However, these metal layers show low thermal conductivity of the range of 54-167 W/mK, and the lower coefficient further in a higher temperature so that the heat transfer characteristics could not be improved enough to be required for the heating or cooling.